Ultraviolet light stabilized, zinc oxide pigmented, 1-olefin resin composition



States Patent Ofifice 3,376,250 Patented Apr. 2, 1968 3,376,250 ULTRAVIOLET LIGHT STABILIZED, ZINC OXIDE PIGMENTED, l-OLEFIN RESIN COMPOSITION Gordon C. Newland and John W. Tamblyn, Kingsport,

Tenn., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Jan. 22, 1965, Ser. No. 427,499 Claims. (Cl. 260-41) ABSTRACT OF THE DISCLOSURE A normally solid, white, thermoplastic composition for shaping into articles comprising (1) polyethylene or a co polymer of propylene and butene-l, (2) a pigmenting amount of zinc oxide, and (3) a stabilizing amount of zinc N,N-dialkyldithiocarbamate or 2,6-didodecyl-p-cresol when (l) is polyethylene, or a stabilizing amount of zinc N,N-dialkyl-dithiocarbamate or dialkyl 3,3 thiodipropionate when (1) is a copolymer of propylene and butene-l.

This invention resides in the chemical arts. It relates to synthetic resins and to the problem of inhibiting their deterioration under ultraviolet light.

Normally solid polymers of l-olefins, such as normally solid polyethylene and crystalline polypropylene, are thermoplastic synthetic resins which have gained wide spread use as materials of construction. However, as is well known, normally solid, l-olefin resins undergo photochemical degradation when exposed to ultraviolet light. This effect is frequently termed weathering. It appears to be a photooxidation process which causes rupture of the polymer chains and formation of carbonyl (=C=O) groups. As this degradation progresses, articles manufactured from l-olefin resins tend to crack, become brittle and lose tensile strength to the extent of mechanical failure.

White plastic compositions are often wanted. Such compositions are normally made by incorporating a white pigment such as finely divided zinc oxide, finely divided titanium dioxide and the ilke into plastics by conventional mixing procedures. Unfortunately, these pigments offer very little protection against ultraviolet light degradation. Indeed, when finely divided titanium dioxide, for example, is incorporated into polyethylene, the result is an acceleration of ultraviolet light degradation.

This invention is based upon the discovery that certain mixtures of finely divided zinc oxide and specific organic compounds, when incorporated into particular l-olefin resins, not only enhance the weatherability of these resins, but do so synergistically.

In summary, this invention comprises a normally solid, white, thermoplastic composition consisting essentially of (A) normally solid, l-olefin resin selected from the group consisting of normally solid polyethylene and copolymer of propylene and butene-l, (B) finely divided zinc oxide at a concentration sufiicient to substantially pigment said l-olefin resin and (C) when said l-olefin resin is normally solid polyethylene, 0.14% by weight of said resin of material selected from the group consisting of zinc N,N-di (C -C alkyl)dithiocarbamate and 2,6-didodecyl-p-cresol, and when said l-olefin resin is said copolymer, 0.1-1% by weight of said resin of material selected from the group consisting of zinc N,N-di(C C alkyl)dithiocarbamate and dilauryl 3,3'-thiodipropionate.

Normally solid polyethylene and normally solid copolymer of propylene and l-butene are well known l-olefin resins and, therefore, need not be further described herein.

Zinc oxide is a well known white pigment. In general, it is a finely divided solid. A concentration of finely divided zinc oxide in the composition of this invention generally at about 0.2510% by weight of the l-olefin resin is usually sufficient to substantially pigment it.

The remaining components of the basic composition of this invention are well known compounds and, therefore, need not be further described herein.

The normally solid, thermoplastic composition of this invention can also comprise other additives such as, for example, antioxidants, heat stabilizers, additional ultraviolet light inhibitors, anticorrosion additives, antistatic agents, foaming agents, plasticizers, waxes, mold release agents, slip agents, anti-blocking agents, fillers, extenders and the like, including physical property improvers other than polymeric compounds.

The plastic composition of this invention is made by incorporating the components thereof into the l-olefin resin. Generally such incorporation is performed by any one of a number of well known methods, such as roll compounding, extrusion, solvent mixing and the like. For example, such incorporation can be performed by heating or otherwise softening the l-olefin resin to a workable consistency and then Working in as by roll compounding until a substantially uniform mixture or dispersion is obtained.

The resulting plastic composition of this invention is then usually formed into articles such as pellets, sheeting, films, bars, tubes, filaments, specially shaped articles and the like as by conventional casting and molding techniques which include extrusion, compression molding, blow molding and the like.

This invention is further illustrated by the following examples of various aspects thereof including specific embodiments. Unless otherwise indicated this invention is not limited to these specific embodiments.

illustrate specific embodiments of a composition according to this inven- Concentration in Components Parts by Wt.

Ex. 1 Ex. 2 Normally solid polyethylene Finely divided zinc oxide. 10 Zinc N,N-dibutyldithiocarbam 2 .fi-didodecyLp-r resol 0. 5

These specific embodiments are made by admixing the components for 4 minutes on hot compounding rolls, the front roll being at 270 F. and the rear roll at 220 F.

The products thus obtained are white polyethylene compositions useful in articles likely to be exposed to ultraviolet light.

Examples 34 These examples illustrate specific embodiments of a white composition according to this invention, which is based on copolymer of propylene and l-butene.

These specific embodiments are formulated as follows:

Concentration in Zinc N,N-dibutyldithiocarbaiziate 1 Dilauryl 3,3-thiodipropionate "QIIIIIII These specific embodiments are made by admixing the components for four minutes on hot compounding rolls, the front roll being at 320 F. and the rear roll at 285 F.

The products thus obtained are useful in shaped articles 3 4 likely to be exposed under normal use conditions to developed stress cracks the stress crack free life of the ultraviolet light. sample was calculated. The stress crack free life is the i Samples of the composition of this invention have averaged exposure time required for all three specimens actually been tested for ultraviolet light stability. In the to develop stress cracks. The test data of the samples i first series of tests, samples were made from a conreported herein are summarized in the following table.

Concentration in Parts by Weight,

Components Samplel SampleZ Sarnpleli Samples Samplefi Samplofi Normally solid copolymer 100 100 100 100 100 Zinc oxide 10 l0 10 Zinc N,N*dibutyldithiocarbamate.. 1.0 1.0

Dilauryl 3,3'-thiodiproprionste 10. 0 1.0

Hours Stress crack tree life 147 162 238 185 l, 130 l, 160

ventional, low density, normally solid polyethylene having These data show that samples 5 and 6 correspond to the a melt index of 2. The samples were made by the prospecific embodiments of Examples 3 and 4. Samples 5 and cedure described in connection with Examples l2 and 6 are not only substantially stabilized relative to ultraincluded samples formulated as indicated in the folviolet light, but are so stabilized by the synergistic coaclowing table. Flat plates of 125 mils thickness were comtion between zinc oxide and. the organic compounds. pression molded from the samples and three test speciadded. mens 1.5 x 0.5 inch were cut from the molded plates. Thus, this invention provides a White thermoplastic The test specimens were bent into U-shape and while composition having a substantial degree of stability thus stressed mounted upside down in a /2 inch wide 5 against ultraviolet light. channel. The stress test specimens while mounted in the Other features, advantages and embodiments of this channel were then placed in an Atlas Twin-Arc Weatherinvention will be apparent to those in the exercise of or- Ometer [AnaL Chem. 25, 460 (1953)]. While exposed dinary skill in the art after reading the foregoing disclothe specimens were periodically inspected for the desures. In this connectiomwhile specific embodiments of velopment of cracks visible under 3X magnificationv this invention have been described in considerable detail, When such stress cracks were observed in a specimen, variations and modifications of these embodiments can the exposure time for that specimen was determined. be effected without departing from the spirit and scope When all three specimens of a sample had developed of the invention as disclosed and claimed. stress cracks, the stress crack free life of the sample was We claim: then calculated, it being the averaged exposure time 1. A normally solid, white, thermoplastic composition required for all thre specimens to develop stress cracks. consisting essentially of (A) normally solid, l-olefin resin Test data for the samples reported herein are sumselected from the group consisting of normally solid polymarized in the following table. ethylene and copolymer of propylene and butene-l at a Concentration in Parts by Weight Components Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample (5 Normally solid polyothylene. 100 100 100 100 100 100 Finely divided zinc oxide l0 10 10 Zinc N,N-dihutyldithiocarb mate O. 5 0 5 2,6-didodecyl-p-cresol 0. 5 0. 5

Hours Stress crack free life 300 300 320 330 1.850 1. 100

Samples 5 and 6 correspond to the specific embodiweight ratio of propylene to butene-l of 80:20, (8) ments of Examples 1 and 2. finely divided zinc oxide at a concentration of about 0.25

From these data it can be seen that the compositions 10% by weight of said l-olefin resin and (C) when of this invention have a substantial degree of stability said l-olefin resin is normally solid polyethylene 0.ll% relative to ultraviolet light. Moreover, the data show by weight of said resin of material selected from the that in the compositions of this invention zinc oxide and group consisting of zinc N,N-dibutyldithiocarbamate and the other additives cooperate synergistically to inhibit 2,6-didodecyl-p-cresol and when said l-olefin resin is said the ultraviolet light deterioration of polyethylene. copolymer 0.l-1% by Weight of said resin of material so- In another series of tests samples were made from a lected from the group consisting of zinc N,N-dibutyldinormally solid copolymer of propylene and l-butene at thiocarbamate and dilauryl 3,3-thiodipropionate.

a weight ratio of propylene to l-butene of 80:20. The 2. A normally solid, white, thermoplastic composition normally solid copolymer had a density of 0.889 and an consisting essentially of normally solid polyethylene, inherent viscosity of 2.35. The samples were made acfinely divided zinc oxide at a concentration of about cording to the procedure described in connection with 0.25-l0% by weight of said polyethylene and zinc, N,N-.

Examples 3-4. The samples made included the samples dibutyldithiocarbamate at a concentration of about formulated as indicated in the following table. The 0.l-1% by weight of said polyethylene.

product obtained in each case was compression molded 3. A normally solid, white, thermoplastic composition into a flat plate 125 mils thick. Three test specimens 1.5 consisting essentially of normally solid polyethylene, fineinches x 0.5 inch were cut from the molded plate of ly divided zinc oxide at a concentration of about 0.25 to each sample, bent into U-shape and while thus stressed about 10% by weight of said polyethylene and 2,6-dimounted into a 0.5 inch wide channel. The channel was 7 dodecyl-p-cresol at a concentration of about 01-10% by then placed into a modified Atlas Twin-Arc Weather- 0 weight of said polyethylene.

Ometer. The specimens were periodically inspected for 4. A normally solid, white, thermoplastic composition the development of stress cracks visible under 3 consisting essentially of (A) normally solid, l-olefin resin magnification. When each specimen was observed to selected from the group consisting of normally solid polyhave developed stress cracks, the exposure time for that ethylene and copolymers of propylene and butene-l at a specimen was calculated. When all three specimens had weight ratio of propylene to butene-l of :20, (E) finely 5 6 divided zinc oxide at a concentration of about 0.25-10% 3,001,969 9/1961 Tholstrup 2604575 by Weight of said l-olefin resin, and (C) 0.1-1% by 3,111,499 10/1963 H6I1Ck 260-41 weight of said resin of zinc N,N-dibutyldithiocarbamate. 2,519,755 8/1950 Gribolns 26041 5. A shaped article of composition according to claim 1. 0 ,225 7/ 1957 Hardlng 260-41 5 OTHER REFERENCES References Cited UNITED STATES PATENTS 2,582,510 1/1952 Stiratelii 26045-75 2,972,596 2/1961 Newland 260-45-75 JULIUS J 'y Exammer- Raff: High Polymers, v01. XX, 1964, part II, p. 382 and 383, copy in S. L. 

